In the manufacture of soda ash, a system of storage ponds has been used to accommodate large accumulation of waste water and by-products. These ponds are used to impound insolubles (grits and muds) contained in mined ore; reject impurities from the crystallizer systems; dispose of mine waste water and various plant utility system wastes; and provide cooling for the evaporator trains of the soda ash facility. The waste streams fed to these ponds contain a significant amount of soda value, along with various impurities such as NaHCO.sub.3, Na.sub.2 SO.sub.4, NaCl, SiO.sub.2, C, etc. As the pond water cools, sodium carbonate decahydrate is precipitated in the ponds, which significantly reduces the total pond volume. This reduction in volume results in two major problems for a facility of substantial commercial size; first, the need for additional waste cells to impound insolubles; and second, inadequate evaporation and hence inadequate cooling of the water used for cooling purposes.
Accordingly there exists a need to alleviate this problem of vast accumulations of waste from soda ash manufacture, and numerous methods have been proposed to attain this goal. A further desirable object in addition to reducing waste accumulations, would be to recover the soda value lost to the pond. To do this effectively, however, it is necessary to reject the impurities found in the pond water, a major component of which is sulfate impurities.